High temperature tribological properties of laser <i>in-situ</i> synthesized self-lubricating composite coating on Ti6Al4V alloy

Abstract

In order to improve the high temperature tribological properties of Ti6Al4V alloy, multi-phase hybrid metal matrix high-temperature self-lubricating anti-wear composite coating was in-situ synthesized by laser clad with the powder precursor of Ni60-16.8%TiC-23.2%WS2(mass fraction, the same below). The microstructure, phase composition and tribological properties as well as the corresponding wear mechanisms of the composite coating at 20, 300, 600, 800℃ were analyzed systematically. The results show that the microhardness of the composite coating (701.88HV0.5) is about two-fold of the substrate (350HV0.5). Due to the synergetic effect of the in-situ synthesized solid lubricants Ti2SC/TiS/NiS/TiO/TiO2/NiCr2O4/Cr2O3 and hard phases (W,Ti)C1-x/TiC/Cr7C3, both the wear resistant and friction reducing capabilities of the composite coating are better than that of the substrate. With the increase of temperature, the friction coefficient and wear rates of the composite coating and the substrate all exhibit decreasing trend, i.e., the friction coefficient of the composite coating and substrate are 0.32, 0.43 and wear rates are 1.80×10-4, 2.92×10-5mm/Nm at 800℃, respectively. The main wear mechanisms of substrate are mainly plastic deformation and delamination as well as oxidation wear, while the composite coating is predominated by the oxidation wear and slight adhesive wear at 800℃.

Keywords

• laser cladding
• Ti6Al4V alloy
• high-temperature wear resistant composite coating
• solid lubrication
• <i>in-situ</i> synthesis